MQTT sensor timestamp extraction

[ievren]

Feedback

Title: Clarification Needed on Extracting Timestamps from MQTT Sensors

Description:

I don't understand how to extract the timestamp from a sensor, and it's not very clear to me based on the current documentation.

There is an example explaining processing timestamps, but I am not 100% sure if my approach is correct:

• MQTT Sensor - Processing Unix Epoch Timestamps

I would appreciate it if there were a clear example of how to handle a scenario where a sensor wakes up and sends multiple time points. Is this not a common approach (for battery saving)?

Here's my specific case:

1. Topic: enviro/enviro-urban
2. Message payload:

   {
     "readings": {
       "pressure": 964.46,
       "pm1": 7,
       "pm2_5": 9,
       "noise": 0.036,
       "humidity": 31.65,
       "temperature": 31.53,
       "pm10": 10
     },
     "nickname": "enviro-urban",
     "model": "urban",
     "uid": "e66164084356202d",
     "timestamp": "2024-07-13T21:44:07Z"
   }

To handle this, I manually added the following section to configuration.yaml using the file editor:

mqtt:
  sensor:
    - name: "Enviro Urban Temperature"
      state_topic: "enviro/enviro-urban"
      unit_of_measurement: "°C"
      value_template: "{{ value_json.readings.temperature }}"
      json_attributes_topic: "enviro/enviro-urban"
      json_attributes_template: "{{ {'timestamp': value_json.timestamp} | tojson }}"
      expire_after: 3600
      force_update: true
    
    - name: "Enviro Urban Humidity"
      state_topic: "enviro/enviro-urban"
      unit_of_measurement: "%"
      value_template: "{{ value_json.readings.humidity }}"
      json_attributes_topic: "enviro/enviro-urban"
      json_attributes_template: "{{ {'timestamp': value_json.timestamp} | tojson }}"
      expire_after: 3600
      force_update: true

    - name: "Enviro Urban Pressure"
      state_topic: "enviro/enviro-urban"
      unit_of_measurement: "hPa"
      value_template: "{{ value_json.readings.pressure }}"
      json_attributes_topic: "enviro/enviro-urban"
      json_attributes_template: "{{ {'timestamp': value_json.timestamp} | tojson }}"
      expire_after: 3600
      force_update: true
    
    - name: "Enviro Urban Noise"
      state_topic: "enviro/enviro-urban"
      unit_of_measurement: "V"
      value_template: "{{ value_json.readings.noise }}"
      json_attributes_topic: "enviro/enviro-urban"
      json_attributes_template: "{{ {'timestamp': value_json.timestamp} | tojson }}"
      expire_after: 3600
      force_update: true
    
    - name: "Enviro Urban PM1"
      state_topic: "enviro/enviro-urban"
      unit_of_measurement: "µg/m³"
      value_template: "{{ value_json.readings.pm1 }}"
      json_attributes_topic: "enviro/enviro-urban"
      json_attributes_template: "{{ {'timestamp': value_json.timestamp} | tojson }}"
      expire_after: 3600
      force_update: true

    - name: "Enviro Urban PM2.5"
      state_topic: "enviro/enviro-urban"
      unit_of_measurement: "µg/m³"
      value_template: "{{ value_json.readings.pm2_5 }}"
      json_attributes_topic: "enviro/enviro-urban"
      json_attributes_template: "{{ {'timestamp': value_json.timestamp} | tojson }}"
      expire_after: 3600
      force_update: true
    
    - name: "Enviro Urban PM10"
      state_topic: "enviro/enviro-urban"
      unit_of_measurement: "µg/m³"
      value_template: "{{ value_json.readings.pm10 }}"
      json_attributes_topic: "enviro/enviro-urban"
      json_attributes_template: "{{ {'timestamp': value_json.timestamp} | tojson }}"
      expire_after: 3600
      force_update: true
    
    - name: "Enviro Urban Voltage"
      state_topic: "enviro/enviro-urban"
      unit_of_measurement: "V"
      value_template: "{{ value_json.readings.voltage }}"
      json_attributes_topic: "enviro/enviro-urban"
      json_attributes_template: "{{ {'timestamp': value_json.timestamp} | tojson }}"
      expire_after: 3600
      force_update: true

It may be related to this discussion:

• Home Assistant Community - Sensor Transmits Multiple Time Points
• GitHub - Pimoroni/enviro Issues #227

Would it be possible to get a clear example or further guidance on this?

URL

https://www.home-assistant.io/integrations/sensor.mqtt/

Version

2024.7.2

Additional information

No response

[home-assistant]

Hey there @emontnemery, @jbouwh, @bdraco, mind taking a look at this feedback as it has been labeled with an integration (mqtt) you are listed as a code owner for? Thanks!

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[jbouwh]

I would not recommend using json attributes with changing values on every update, and neither, I would encourage not to set force_update. Both will have a negative impact on the performance as all entities will enforce a state write when an update is received. I you want to have a timestamp in a sensor, I suggest to add a timestamp sensor for it instead.
Assign timestamp as the sensor's device_class.

For the question on multiple time points of data in the past:
Home Assistant assumes incoming sensor data is actual data. I do not know of any support to import a time series of data into Home Assistant yet. You could consider using Influx DB to import/store such data.

[ievren]

@jbouwh, thank you for your answer.

Thank you for clarifying this. It was not clear to me that Home Assistant assumes incoming sensor data is actual data. We can consider this matter resolved